Acetyl-L-carnitine or ALCAR, is an acetylated form of L-carnitine. It is naturally produced by the body, although it is often taken as a dietary supplement. Acetylcarnitine is broken down in the blood by plasmaesterases to carnitine which is used by the body to transport fatty acids into the mitochondria for breakdown.[2]

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ALCAR is an acetylated derivative of L-carnitine. During strenuous exercise, a large portion of L-carnitine and unused acetyl-CoA are converted to ALCAR and CoA inside mitochondria by carnitine O-acetyltransferase.[2][3] The ALCAR is transported outside the mitochondria where it converts back to the two constituents. The L-carnitine is cycled back into the mitochondria with acyl groups to facilitate fatty acid utilization, but excess acetyl-CoA may block it.[4][5] Excess acetyl-CoA causes more carbohydrates to be used for energy at the expense of fatty acids. This occurs by different mechanisms inside and outside the mitochondria. ALCAR transport decreases acetyl-CoA inside the mitochondria, but increases it outside.[6][7] Glucose metabolism in diabetics improves with administration of either ALCAR[8] or L-carnitine.[9] ALCAR decreases glucose consumption in favor of fat oxidation in non-diabetics.[10] A portion of L-carnitine is converted to ALCAR after ingestion in humans.[11]

It has been claimed ALCAR is superior to L-carnitine in terms of bioavailability.[2][12] Both use the same mechanism for intestinal absorption that improves with sodium.[13] One study shows ALCAR has a lower blood concentration in humans after ingestion[14] possibly because ALCAR is hydrolyzed more in blood.[15]

Early research which seemed to suggest Acetylcarnitine had potential as a treatment for dementia were not strongly substantiated by later research, and the substance is not routinely used for this purpose.[16]

^Rebouche CJ (November 2004). "Kinetics, pharmacokinetics, and regulation of L-carnitine and acetyl-L-carnitine metabolism". Annals of the New York Academy of Sciences1033: 30–41. doi:10.1196/annals.1320.003. PMID15591001.